Let's call the amount of blue files x, so the amount of yellow files is 2x and the amount of red files is 3+x. The sum of these is 4x+3= 85. Solving for x, we get the amount of blue files as 20.5 which means there are x+3= 23.5 red files.
Since you can't have part of a file, I think there is something wrong with your question, the numbers don't add up correctly.
Hope it helps!
You can see this answer:
Although the question is a little different, it has a good explanation.